A cellulose acetate film has lower optical anisotropy and thus provides lower retardation in comparison with other polymer films. Therefore, it is used in a polarization film or the like.
Recently, a liquid crystal display is increasingly required to have picture improvement and high functions, and a material therefor, that is, a cellulose acetate film for a polarization film is also required to have characteristics satisfying this. Particularly, with respect to an in plain switching (IPS) mode liquid crystal display, as one method for solving chromaticity shift problems and improving contrast ratio, a cellulose acetate film is required to have a low optical anisotropic value (Re: retardation value in-plane of the film, Rth: retardation value in the thickness direction of the film).
The cellulose acetate film has relatively low retardation, but may not achieve a low degree of retardation, which is requested as a retardation film, and thus, a retardation regulator needs to be added. WO 2009/031464 discloses that in cellulose acylates having a total acyl substitution degree of 2.7˜2.95, several kinds of materials having different substitution degrees with respect to a sugar ester compound, in which hydroxy groups of monosaccharide˜trisaccharide are partially esterfied, are mixed and used as a retardation regulator.
However, problems such as bleeding and the like may occur at the time of adding the retardation regulator, and thus a measure for improving this is needed.